In fluid media environments, in particular, in analysis of fluids originating from the human body or of fluids destined for insertion into the human body, such as dialysate, haemodiafiltration fluid or blood serum, but also in plant process environments, in the production of desalinated water etc, a desire exists to monitor the fluids' chemical composition or concentrations, in particular of electrolytes and other chemical traces. Common solution for this are in-line conductivity measurement or off-line analytical testing of fluid samples. With a recent progress of laser technology, compact pulsed lasers are becoming available that combine high beam quality with high pulse energy. When carefully focused, such lasers can deliver energy densities that are strong enough to induce optical breakdown in liquids (in the order of 10×e10 W/cm2).
In fluid media it is possible to generate a short lived plasma wherein the emission spectrum is indicative for the plasma composition.
Spectroscopy techniques of these kinds have been demonstrated in “Laser-induced breakdown spectroscopy (LIBS): “An overview of recent progress and future potential for biomedical applications”, Rehse et al, Journal of Medical Engineering & Technology, 2012: 36 (20; 77-89). However, many of the applications known to date require complex large and costly arrangements for laser focusing and sensing, in particular since photospectrometers (due to their limited etendue) can only detect a very low portion of the total radiation emitted by the plasma. LIBS systems are generally complex, but this holds even more for fluid systems, where the media itself may hinder effective propagation of emission radiation.
Furthermore, a problem in the art of LIBS is the high energy photon flux that passes through the laser entrance window. A desire exists to provide for an effective and simple constitution to effectively measure the chemical concentration of substances of interest in a fluid medium whilst avoiding optically induced damage to the laser entry wall. For this the inventors sought a solution.